... That entirely depends on what card you have.
Google your graphics card (i.e. if it's an Nvidia 670, google "nvidia 670 drivers")
Click on the first link that's from the card's maker (nvidia or radeon), and follow the instructions on that page.
For the other two, google your motherboard and find the manufacturer's support page for that - there will be a downloads section with the drivers you need.
(Just curious, how do people find their way to post on here before they can find the answer on google? Makes no sense to me...)